1. Field of the Invention
The present invention relates generally to methods and compositions for the respiratory delivery of insulin to diabetic patients. More particularly, the present invention relates to the pulmonary delivery of dry powder insulin preparations for rapid systemic absorption through the lungs.
Insulin is a 50 amino acid polypeptide hormone having a molecular weight of about 6,000 which is produced in the pancreatic .beta.-cells of normal (non-diabetic) individuals. Insulin is necessary for regulating carbohydrate metabolism by reducing blood glucose levels, and a systemic deficiency causes diabetes. Survival of diabetic patients depends on the frequent and long-term administration of insulin to maintain acceptable blood glucose levels.
Insulin is most commonly administered by subcutaneous injection, typically into the abdomen or upper thighs. In order to maintain acceptable blood glucose levels, it is often necessary to inject insulin at least once or twice per day, with supplemental injections of rapid-acting insulin being administered when necessary. Aggressive treatment of diabetes can require even more frequent injections, where the patient closely monitors blood glucose levels using home diagnostic kits. The present invention is particularly concerned with the administration of rapid acting insulins which are able to provide serum insulin peaks within one hour and glucose troughs within 90 minutes.
The administration of insulin by injection is undesirable in a number of respects. First, many patients find it difficult and burdensome to inject themselves as frequently as necessary to maintain acceptable blood glucose levels. Such reluctance can lead to non-compliance, which in the most serious cases can be life-threatening. Moreover, systemic absorption of insulin from subcutaneous injection is relatively slow, frequently requiring from 45 to 90 minutes, even when fast-acting insulin formulations are employed. Thus, it has long been a goal to provide alternative insulin formulations and routes of administration which avoid the need for self-injection and which can provide rapid systemic availability of the insulin.
A variety of such alternative insulin administration roots have been proposed, including intranasal, intrarectal, and intravaginal.
While these techniques avoid the discomfort and poor compliance associated with subcutaneous injection, they each suffer from their own limitations. Intrarectal and intravaginal are inconvenient, uncomfortable, and the latter is not available to the entire population of diabetics. Intranasal delivery would be convenient and probably less objectionable than injection, but requires the use of potentially toxic "penetration enhancers" to effect passage of insulin across the nasal mucosa, which is characterized by a thick epithelial layer which is resistant to the passage of macromolecules. Of particular interest to the present invention is pulmonary insulin delivery where a patient inhales an insulin formulation and systemic absorption occurs through the thin layer of epithelial cells in the alveolar regions of the lung. Such pulmonary insulin delivery appears to provide more rapid systemic availability than does subcutaneous injection and avoids the use of a needle. Pulmonary insulin delivery, however, has yet to achieve widespread acceptance. Heretofore, pulmonary delivery has been most often accomplished through nebulization of liquid insulin formulations, requiring the use of cumbersome liquid nebulizers. Moreover, the aerosols formed by such nebulizers have a very low insulin concentration, necessitating a large number of inhalations to provide an adequate dosage. Insulin concentration is limited due to the low solubility of insulin in suitable aqueous solutions. In some cases, as many as 80 or more breaths may be required to achieve an adequate dosage, resulting in an administration time from 10 to 20 minutes, or more.
It would be desirable to provide improved methods and compositions for the pulmonary delivery of insulin. It would be particularly desirable if such methods and compositions were sufficiently convenient to permit self-administration even away from home and were able to deliver a desired total dosage with a relatively low number of breaths, preferably fewer than ten. Such methods and compositions should also provide for rapid systemic absorption of the insulin, preferably reaching a serum peak within 45 minutes or less and a resulting glucose trough within about one hour or less. Such rapid acting formulations will preferably be suitable for use in aggressive treatment protocols where injection of intermediate and long-acting insulin can be reduced or eliminated. The compositions of the present invention should also be stable, preferably consisting of a concentrated dry powder formulation.
2. Description of the Background Art
The respiratory delivery of aerosolized aqueous insulin solutions is described in a number of references, beginning with Gansslen (1925) Klin. Wochenschr. 4:71 and including Laube et al. (1993) JAMA 269:2106-21-9; Elliott et al. (1987) Aust. Paediatr. J. 23:293-297; Wigley et al. (1971) Diabetes 20:552-556. Corthorpe et al. (1992) Pharm Res 9:764-768; Govinda (1959) Indian J. Physiol. Pharmacol. 3:161-167; Hastings et al. (1992) J. Appl. Physiol. 73:1310-1316; Liu et al. (1993) JAMA 269:2106-2109; Nagano et al. (1985) Jikeikai Med. J. 32:503-506; Sakr (1992) Int. J. Phar. 86:1-7; and Yoshida et al. (1987) Clin. Res. 35:160-166. Pulmonary delivery of dry powder medicaments, such as insulin, in a large particle carrier vehicle is described in U.S. Pat. No. 5,254,330. A metered dose inhaler (MDI) for delivering crystalline insulin suspended in a propellant is described in Lee and Sciara (1976) J. Pharm. Sci. 65:567-572. A MDI for delivering insulin into a spacer for regulating inhalation flow rate is described in U.S. Pat. No. 5,320,094. The intrabronchial administration of recombinant insulin is briefly described in Schluter et al. (Abstract) (1984) Diabetes 33:75A and Kuhler et al. (1987) Atemw. Lungenkrkh. 13:230-232. Intranasal and respiratory delivery of a variety of polypeptides, including insulin, in the presence of an enhancer, are described in U.S. Pat. No. 5,011,678 and Nagai et al. (1984) J. Contr. Rel. 1:15-22. Intranasal delivery of insulin in the presence of enhancers and/or contained in controlled release formulations are described in U.S. Pat. Nos. 5,204,108; 4,294,829; and 4,153,689; PCT Applications WO 93/02712, WO 91/02545, WO 90/09780, and WO 88/04556; British Patent 1,527,605; Ryden and Edman (1992) Int. J. Pharm. 83:1-10; and Bjork and Edman (1988) Int. J. Pharm. 47:233-238. The preparation and stability of amorphous insulin were described by Rigsbee and Pikal at the American Association of Pharmaceutical Sciences (AAPS), Nov. 14-18, 1993, Lake Buena Vista, Fla. Methods for spray drying polypeptide, polynucleotide and other labile drugs in a carrier which forms an amorphous structure which stabilize the drug are described in European patent application 520 748.